CC1021-RTR1 datasheet(53/91 Pages) TI1

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XTAL

XOSC_Q2

XOSC_Q1

parasitic

Not Recommended for New Designs NRND

CC1021

www.ti.com

SWRS045D – JANUARY 2006 – REVISED JANUARY 2015

Using the internal crystal oscillator, the crystal must be connected between the XOSC_Q1 and XOSC_Q2

pins. The oscillator is designed for parallel mode operation of the crystal. In addition, loading capacitors

(C4 and C5) for the crystal are required. The loading capacitor values depend on the total load

capacitance, CL , specified for the crystal. The total load capacitance seen between the crystal terminals

should equal CL for the crystal to oscillate at the specified frequency.

(33)

The parasitic capacitance is constituted by pin input capacitance and PCB stray capacitance. Total

parasitic capacitance is typically 8 pF. A trimming capacitor may be placed across C5 for initial tuning if

necessary.

The crystal oscillator circuit is shown in Figure 5-30. Typical component values for different values of CL

are given in Table 5-15.

The crystal oscillator is amplitude regulated. This means that a high current is required to initiate the

oscillations. When the amplitude builds up, the current is reduced to what is necessary to maintain

approximately 600 mVpp amplitude. This ensures a fast start-up, keeps the drive level to a minimum and

makes the oscillator insensitive to ESR variations. As long as the recommended load capacitance values

are used, the ESR is not critical.

The initial tolerance, temperature drift, aging and load pulling should be carefully specified in order to meet

the required frequency accuracy in a certain application. By specifying the total expected frequency

accuracy in SmartRF Studio together with data rate and frequency separation, the software will estimate

the total bandwidth and compare to the available receiver channel filter bandwidth. The software will report

any contradictions and a more accurate crystal will be recommended if required.

Figure 5-30. Crystal Oscillator Circuit

Table 5-15. Crystal Oscillator Component Values

ITEM

CL = 12 pF

CL = 16 pF

CL = 22 pF

6.8 pF

15 pF

27 pF

6.8 pF

15 pF

27 pF

5.17 Built-in Test Pattern Generator

The CC1021 has a built-in test pattern generator that generates a PN9 pseudo random sequence. The

PN9_ENABLE bit in the MODEM register enables the PN9 generator. A transition on the DIO pin is

required after enabling the PN9 pseudo random sequence.

The PN9 pseudo random sequence is defined by the polynomial x9 + x5 + 1.

The PN9 sequence is ‘XOR’ed with the DIO signal in both TX and RX mode as shown in Figure 5-31.

Hence, by transmitting only zeros (DIO = 0), the BER (Bit Error Rate) can be tested by counting the

number of received ones.

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